1. Field of the Invention
This invention relates to an abutment tooth model and a method of manufacturing a prosthetic restoration to be formed on the abutment tooth model.
2. Description of the Prior Art
There are known prosthetic restorations. A prosthetic restoration is used by being attached to an abutment tooth which has been formed by giinding down a living tooth in the oral cavity. The prosthetic restoration is used by being bonded to and fixed on the abutment tooth with a dental cement.
Both (1) metals such as gold, silver and stainless steel and (2) ceramics such as zirconia, alumina and sapphire have been so far used as structural materials for such prosthetic restorations.
However, prosthetic restorations made of ceramic materials have a disadvantage in that they have lower toughness and therefore are liable to be damaged.
Furthermore, prosthetic restorations made of noble metals such as gold and silver are very expensive. Moreover, prosthetic restorations made of stainless steel have poor biocompatibility, so that they may have an adverse effect on the body such as the onset of metal allergies or the risk of carcinogenic actions due to the elusion of Ni and Cr in particular.
In view of the problems as described above, prosthetic restorations made of Ti (titanium) have been developed in recent years. Ti is light and very strong and has excellent corrosion resistance, and it does not give rise to adverse effects due to eluting materials as described above.
The prosthetic restorations made of Ti are manufactured as follows.
Firsts an abutment tooth model corresponding to the abutment tooth which has been prepared in the oral cavity is made from an ultra-hard plaster. Next, a compound containing Ti powder is built up onto the abutment tooth model to form a green body for a prosthetic restoration, and then the green body is subjected to a binder removal treatment. Thereafter, the green body is sintered together with the abutment tooth model. In this way, the prosthetic restoration comprised of a metal sintered body is obtained.
However, in the conventional manufacturing method for the prosthetic restorations, there is a disadvantage that the obtained prosthetic restoration is fragile and its mechanical strength is low, because Ti contained in the green body is reacted with the ultra-hard plaster during sinteling process so that an oxygen content at a portion of the prosthetic restoration to be in contact with the abutment tooth model increases.
Further, the prosthetic restoration is likely to be bonded to the abutment tooth model when being sintered due to the reaction between the Ti and the ultra- hard plaster As a result, there is a problem in that it becomes difficult to release the sintered prosthetic restoration from the abutment tooth model. Further, there is also a problem in that a reaction product is peeled off from the abutment tooth model and then it is attached to the prosthetic restoration, when the sintered prosthetic restoration is released from the abutment tooth model.
The attached reaction product causes changes in the property of the prosthetic restorations. Further, the reaction product is by nature unnecessary. Therefore, the reaction product is required to be removed. However, the removal operation of the reaction product is quite troublesome and the remainder thereof lowers the quality of the prosthetic restoration.